Hydraulic pressure system



Jan.9,1923. 1,441,758. mascuwmmm.

HYDRAULIC PRESSURE SYSTEM FILED MAR. 4. 1920.

2 SHEEIS--SHEET l.

- flnv@nt@1r: Charl Jan.- 9, 1923 C. F. SCHWENNKER.

LMLTSS.

FILED MAR;4.1v920.

2 SHEEI'S-SHEET 2.

57 F; g. a. @o

Inventor:

His Attornnay.

Fatentetll Tan. 9, 1933.

.1 itii' 1.11?

CHARLES E. SCHWJENNKJER, SCHJENJECTAJDY, NEW YORK, ASSIGNOR TU GENERAL ELECTRIC COMPANY, A CORPORATION 01E NEW YORK.

HYDRAULIC rEESsnEE SYSTEM.

Application filed March 4, 1920. Serial No. 363,174.

To all whom it may concern: 1

Be it known that T, CiiAnLns F. bionwnnmmn, a citizen of the United States, residing at Schenectady, in the county of @chenectady', State of New York, have invented certain new and useful Tmprovements in HydraulicPressure Systems, of which the following is a specification.

The present invention relates to hydraulic systems such as are used for operating hydraulic presses and the like, and has for its object to provide an improved structure and arrangement in a system of this character.

For a consideration of what 1 believe to be novel and my invention, attention is directed to the accompanying description and the claims appended thereto.

In the drawing, Fig. l is a view of a somewhat diagrammatic. nature, of a system embodying my invention; Fig. 2 is a longitudinal sectional view of an hydraulic operating valve, and Figs. 3, 4 and 5 are sectional views of valve mechanisms utilized.

in my system.

leferring to the drawing, indicates a tank containing the liquid used in the sys tem which, as a matter of convenience, T will hereinafter term oil, although of course, any suitable liquid may be used. 11 indicates a motor which drives a pump structure comprising essentially two pumps, a low pressure pump comprising cylinder 12 and a high pressure pump comprising two cylinders 13 and 14 which are connected in paraL lel. The suction pipes for cylinders 12, 13 and 14 are indicated at 15. 16 and 17 respectively and they are connected by a pipe 18 to tank 10. In suction pipe is a specially arranged suction valve 19 shown in section in Fig. 5.while cylinders 13 and 14 are provided with suction valves of ordinary construction. The discharge pipe of cylin der.12 is indicated at 20. Cylinders 13 and 14 discharge in parallel through discharge pipe 21. Cylinders 12, 13 and 14 are provided with discharge valves of the usual type. Discharge pipe 20 is provided with a non-return valve 22 and is connected by a pipe 23 to a quick relief valve 24, shown in section in Fig. 3. Discharge pipe 21 of pump cylinders 13 and 14 is connected by a pipe 25 to an hydraulic operating valve 26 shown in section in Fig. 2. 7

The hydraulic press comprises a rectangular frame 27 which carries a main cylinder 28 in which is a piston 29. The outer end of piston 29 engages a crossbar 30 which is guided by frame 27 and carries the punch member 31 of the press. Crossbar 30 is held in engagement With piston 29 by suitable springs 32, which springs serve also to bias piston 29 toward the bottom of cylinders 28, e. to the position shown in the drawing. Cross-bar 30 is provided with a recess 3O in which is located an annular die clamp 33 provided at its central portion with a tapered or coneshaped opening 34. Carried by cross-bar 30 is a stop member 30 for limiting the movement of die clamp 33 toward the left. Carried by clamp 33 are two cylinders 35, in which are pistons 36 the outer ends of which rest against bar 30. Pistons 36 have hollow stems 37 which communicate with the interiors of cylinders 35, and such stems are'connected in parallel by pipes 38 and 39 to a pipe 40 which leads to an hydraulic aocumulator 41., 38 and 39" are joints arranged to permit movement of piston 29 and associated parts which move therewith. Tn pipe 40 is a check valve 42 of a special construction as shown in section in 4. Accumulator 41 is shown as comprising a piston 43 which carries the weights 44 of the accumulator and slides in a cylinder 45 to which pipe 40 is connected, This arrangement may be taken as typical of any hydraulic accumulator which is adapted to store up energy and later release it. 46 indicates a split holder adapted to re eive a die in which a piece of material 47 to be operated upon is held, the end of such material projectinginto a socket 48 in the die. Holder 46 is located in a frame havlng a hinged cover 49, and the arrangement is such that when cover 49 is fully closed an elect circuit 50 is osed. Carried by the which slides in a bore in the lower part of having an admission chamber 57 and a discharge chamber 58, communication between them being controlled by a valve 59 adapted to engage a seat 60. Connected to discharge chamber 58 is a pipe 61 which leads back to tank 10. Leading from admission chamber 57 is a pipe 62 which/connects to hydraulic press cylinder 28. Just below chamber 58, valve 59 is enlarged to form a piston 63 casing 56. Valve ,59 has an axially extending hole 64 through it and is counterbored at its lower end to receive a valve 65 which engages a seat on a cup-shaped member 66 threaded over the end of valve 59, a spring 67 normally pressing valve 65 to its seat. Through the center of valve 65 is a small opening 68. Member 66 carries a guide stem 69 which slides in a sleeve 70 threaded into the lower end of casing 56. 71 are U-shaped packings for preventing leakage of fiuid,. and 72 are passages which conduct fluid from a pipe 73 connected to casing 56'to the admission side of valve 65. Pipe 73 is a branch pipe leading from pipe25. Valve 59 is normally held open by a spring 74.

Referring now particularly to Fig. 2, hydraulic operating valves 26 comprises a casing 7 5 having an inlet port 76 to which ipe 25 connects and a discharge port 77 f iom which extends a pipe 78 back to tank 10. In casing is a shoulder 79 against which is clamped an. annular guard shield 80 by means of a sleeve 81. In shield 80 and sleeve 81 are suitable openings for the passage of fluid. In casing 75 in line with port 77 is a perforated sleeve 82 held in place by a cap 83 which threads in the end of casing 75 to close it, the joint between the two being covered by ring 74. In casing 75 and adapted to slide between shield 80 and one end of sleeve 82 isa sleeve valve 85 having openings 86 through its well for the passage of fluid. The left hand endof sleeve valve 85 is enlarged and counterbored to form a cylinder 87 in which is located a piston 88. The end of cylinder 87 is connected by posts 89 to a ring 90 through the center of which extends a rod 91 connected to the outer end of piston 88. Posts 89 extend through openings in a flange 92 which project from piston 88. Surrounding rod 91 and arranged between ring 90 and a nut 93 on the end of the rod is a coiled spring 94 which serves to hold piston 88 in engagement with ring 90 as shown in Fig. 2. Connected to piston 88 is a stem 95 which extends out through the ri ht hand end of casin 75 and is provided with a shoulder 96 which engages casing 75 to limit movement of piston 88 toward the left, the same being biased in this direction by a spring 97 which surrounds cylinder 87 and engages at one end, an end of sleeve 82, and at the other end one side of flange 92. Connected to the outer end of stem 95 is a rectangular latch casing 98 in which is located a catch 99 pivoted on a spindle 100 adapted to move back and forth in a slot 101 in the walls ofcasing 98. Pivoted to casing 75 is an operating handle 102 which is connected to spindle 100 and when moved back and forth, slides latch 99. The end of latch 99 is adapted when raised to engage with an abutment 103 carried by latch casing 98, but when in the position shown in Fig. 2 latch 99, if handle 102 is moved, slides under abutment 103. Latch 99 is arranged to be raised into engagement with abutment 103 by the plunger 104 of an electromagnet 105 located in circuit 50. It will thus be seen that as long as electromagnet 105 is unencrgized. handle 102 when operated, merely moves latch 99 idly back and forth in casing 98. spindle 100 sliding back and forth in slot 101. If, however, the electromagnet 105 is energized, then latch 99 will be raised into engagement with abutment 103 and a movement of lever 102 toward the left will move stem 95, piston 88 and cylinder 87 as a unit toward the right. Between moving parts in casing 75 are suitable packings 106, 107 and 108 to prevent leakage, the same being preferably U-shaped in section as shown.

Referring to Fig. 5, suction valve 19 for pump cylinder 12 comprises a casing 111 having a seat 112 against which a valve 113 is pressed by a spring 114. Fluid enters by the lower section of pipe 15 and leaves by the upper section of pipe 15. Beneath valve 113 is a valve lifting stem 115 connected at its lower end to a lever 116 pivoted on a bracket arm 117. One end of lever 116 carries an adjustable weight 1 18 and the other end is connected to a piston 119 which moves in a cylinder 120. Cylinder 120 is connected by a pipe 121 to the delivery pipe 21 of cylinders 13 and 14. Connected to lever 116 is a rod 116 the upper end of which passes through an opening in the end of an arm 116" carried by accumulator weights 44. On the end or rod 116 is a nut 116, between which and the end of arm 116 is a coiled spring 116.

Referring to Fig. 4, check valve 42 comprises a casing 124 having a scat against which a valve 125 is normally pressed by a spring 126. In the face of valve 125 is a small groove 127. The arrangement is such that fluid can flow quickly through valve 42 metres to the accumulator but to returntherefrom, it must pass slowly through groove 127.

The operation is as follows :-Assume that the motor 11 is driving pump cylinders 12, 13and 14; that operating handle 102 is in the position shown in Figs. 1 and 2, and that the hinged cover 49 is open; also that the switch shown at 130 in circuit 50 is closed. The cylinders 13 and 14 will be drawing oil from tank 10 through the pipe 18 and pipes 16 and 17 respectively and delivering it through pipe 21 and pipe 25 to inlet port 7 6 (Fig. 2) of hydraulic valve 26. The oil flows from inlet port 76 through the openings in sleeve 81 and shield 80, thence along the Space surrounding rod 95 and through openings 86 in sleeve 85 to discharge port 77 from which it passes through pipe 7 8 back to tank 10. It will thus be seen that the pump cylinders 13 and 14, which constitute a high pressure pump,- areidly pumping oil from tank 10 through hydraulic operating valve 26 back to the tank and practically no pressure is set up. Tn other words, pipes 18, 16 and 17, 21, 25 and 78 form a closed fluid circuit through which pump cylinders 13 and.14 may continuously pump fluid. Due to this, the pressure conducted to cylinder 120 through a pipe 121 will be under these circumstances of smallvalueand weight 118 will hold piston 119 in such position that valve lifting stem 115 is .out of engagement with suction valve 113 of the low pressure pump cylinder 12 so that such valve is closed. The low pressure pump cylinder 12 will accordingly be sucking oil through the pipes 18 and 15 and discharge it through pipes 20 and 23 to admission chamber 57 (Fig. of quick return valve 24. Spring 74 at this time is holding valve 59 open so that the oil from admission chamber 57 flows to discharge chamber 58 and thence through pipe 61 back to oil tank 10. Low pressure pump cylinder 12 will he therefore,- running substantially idle and producing but little pressure in the system. However, the pres-- sure will be such that sufficient oil will flow through pipe 62 to cylinder 28 of the hydraulic press to maintain the system filled with oil. As in the case with pump cylinders 13 and 14, pump cylinder 12 has a closed fluid circuit comprising pipes 18, 15, 20, 23 and 61. With hinged cover 49 open, circuit 50 willbe open so that latch 99 lies in the position shown in. Fig. 2. The movement of handle 102 cannot therefore be made to operate the press. lit now a piece 47 upon which work is to be performed is placed iii die 46 and the cover 49 securely closed, then electric circuit 50 is closed with the result that electromagnet 105 is energized lifting its plunger 104 and bringing latch 99 into engagementwith abutment 103. The operator now moves handle lever 102 toward the left, whereupon stem 95 will be the hydraulic press.

moved toward the right carrying with it piston 88, cylinder 87, and sleeve valve 85. As a result openings 86 in sleeve valve 85 .sult fluid pressure will be immediately built up in pipe 25 by pump cylinders 13 and 14 and this pressure, being conveyed through pipe .73 to quick return'valve 24, will acton the lower side of piston 63 to quickly bring valve 59 into engagement with seat 60, the spring 74 being comparatively light. As soon as valve 59 closes, further escape of the oil delivered by pump cylinder 12through pipe 61 back to tank 10 is cut off with the result that pump cylinder 12 starts to deliver oil through pipe 62 to cylinder 28 of This immediately builds up a pressure back of piston 29 and starts-to move it toward the left. Pump cylinder 12, as already stated, is a low pres sure cylinder of comparatively large volume and as a result quickly supplies a considerable volume of oil to cylinder 28 so as to effect a rapid movement of piston 29 which at this time oflers comparatively slight resistance to movement. At the same time the pressure delivered from pump cylinders 13 and 14 opens the small valve 65 of the quick return valve'and oil from pump cylinders 13 and 14 flows past it through hole 64 in valve .59 to pipe 62, so that at this time all three fected by the valve. lifting stem 115 which when the pressure delivered by discharge pipe 21 of cylinders 13 and 14 reaches a predetermined value is raised by piston 119. thereby lifting suction valve 113 off its seat and holding it there, so that pump cylinder 12 will run idly, simply drawing oil in and forcing it back out of pipe 15. The dis chargepressure of pipe 21 is conveyed to cylinder 120 by pipe 121 so that piston 119 is always subjected to the delivery pressure of pump cylinders 13 and 14 and as soon as this delivery pressure reaches a predetermined value, the piston 119 is lowered to lift suction valve 113 off its seat. At this time the end of lever 116 lifts rod 116 the end of which slides through the opening in the end of the arm 116". The non-return valve 22 in pipe 20 prevents flow of oil from hydraulic press cylinder 28 back through pipe 23 and pipe 20 to pump cylinder 12, this valve being in addition to the usual discharge valve of pump cylinder 12. After pump cylinder 12 is rendered inoperative, the high pressure cylinders 13 and 14 alone supply oil through pipe 73, quick return valve 24, and pipe 62 to operate the hydraulic press, the same being utilized for the high pressure required in the final operation.

Referring now particularly to the opera tion of the press, as piston 29 moves toward the left the cone-shaped opening in die clamp 33 moves over the right hand end of die holder 46 to clamp the parts of the die holder together. -At this time the piston 29, cross-bar 30, pistons 36 and die clamp 33 move as a unit-maintaining the relative positions shown in Fig. 1, the die clamp being prevented from moving relatively to the cross-bar 30 due to the hydraulic pressure in cylinders 35, which pressure is maintained by the inertia of the accumulator 41. After die clamp 33 has engaged the right hand end of die holder 46, further movement of piston 29 moves the die holder 46 along with the other moving parts compressing springs 55 behind member 54, and bringing the cpneshaped left hand end of the die holder into die clamp 51. The two ends of die holder 46 i are thus firmly fastened by the die clamps so they cannot under any circumstances spread apart. By this time member 54 has been pressed back until it engages the end of frame 27 and can move no further, thereby giving it solid backing for the die holder 46. The punching tool 31 now engages the piece 47 in the die and performs the work upon it, whatever it may be. At this time the die clamp 33 can move no further toward the left and further movement of piston 29 accordingly moves cross-bar 30 and pistons 36 relatively to die clamp 33. This forces pistons 36 into cylinders 35 and the oil in such cylinders is expelled through the hollow stems 37 to pipes 38 and 39 and thence through pipe 40 and valve 42 to the cylinder 45 of accumulator 41. This acts to raise the piston 43 and weights 44 of the accumulator to store up energy in the accumulator. By this arrangement it will be clear that the accumulator serves to maintain pressure against die clamp 33 to hold it firmly over the end of die holder 46.

During the operation of the press the operator has merely to hold handle 102 in the left hand position to which he has moved it. After the pressure has built up to a predetermined high value in the system, i. e., to a value as high as is desired for the operationof the press'the pressure conveyed through pipe 25 to hydraulic operating valve 26 will become sufliciently great that, operating on the right hand end of sleeve valve and cylinder 87, it will move the same toward the left against the action of spring 94, thereby causing ports 86 in sleeve valve 85 to be partially uncovered, permitting oil to escape once more through pipe 78 back to tank 10, in sufiicient quantities to relieve the excess pressure in the system. By this means, after a predetermined pressure has been reached in the system, such pressure will be automatically maintained but cannot go beyond such value. c ()r, viewed from another aspect, this arrangement of hydraulic operating valve provides an automatic means for stopping the action of the hydraulic press after the desired pressure has been obtained and the work performed. In this connection, it will be noted that sleeve valve 85 is substantially balanced, the differential area upon which fluid pressure acts in moving sleeve valve 85 toward the left being quite small so that a very small volume of oil suffices for effecting the necessary movement of the sleeve valve. This makes the'operation quick and decisive and opens the valve sufliciently to prevent wire drawing and rapid wear.

The work having been performed, the operator moves handle 102 toward the right to its original position thereby bringing the parts of the hydraulic operating valve 26 back to the position shown in Fig. 2. This immediately completely uncovers ports 86 and quickly relieves the pressure in pipe 25 and pipe 73 and hence relieves the pressure under piston 63 whereupon spring 74 immediately opens quick-return valve 59. As a result the oil in cylinder 28 can escape through pipe 62 to chamber 57 of the quick return valve 24, thence to chamber 58 there of and by way of pipe 61 back to tank 10. At this time valve 65 is closed and acts in substance as a non-return valve to prevent oil flowing back through pipe 73. The springs 32 and 55 bring the hydraulic press back to its original position and the crossbars 30 and die clamp 33 are separated by the accumulator 41, the weight of which slowly forces the oil past the small groove 127 in valve 125 through pipe 40 and pipes 38 and 39 to cylinders 35. The purpose of accumulator 41 is to hold the die clamp 33 of the hydraulic press in position over the end of die holder 46 during the latter portion of the stroke of the press, and when the stroke is completed the accumulator serves to force oil back into cylinders 35 and again separate cross-bar 30 and die clamp 33. \Vhen accumulator 41 moves up arm 116" moves with it, thus holding rod 116 in a position to maintain suction valve 113 open. By this arrangement suction valve 113 is held open until the accumulator returns to its normal position. This serves as a means for retarding the closing of suction valve 113 so pump 12 is held out of action until the oil has had a chance to discharge from press cylinder 28.

The groove 127 in valve 125 is preferably quite small so that the return flow of fluid through it is gradual. ith an arrangement of this character I have found that the groove wears practically not at all due to the flow of oil through it and that it is kept clean by thepassage of oil past the valve 125 when oil is flowing from cylinders to the accumulator.

lit will be seen that cylinders 35, pipes 38, 39 and 40 and the accumulator cylinder form a closed hydraulic system, the oil be ing merely forced back and forth from one to the other. This system is alwaysunder considerable pressure and must be kept full of oil. lFor the purpose. ll provide a pipe 131 in which is a -non-return valve 132. With this arrangement the system referred to will be kept filled with oil from pressure pipe 25. 133 is a bypass whereby the pressure in cylinders 35 and the. accumulator may be relieved temporarily, for setting the die, for example. Normally by-pass 133 is closed by valve 134.

Referring now particularly tothe quick return valve 24: shown in Fig. 3, it is to be especially noted that by the arrangement shown, pressure of the hydraulic press is not required to be relieved through the con duit through which the oil is supplied. In other words, the oil is supplied through pressure pipes 23 and 73 but is relieved through waste pipe 61. The purpose of the small opening 68 in valve 65 is to equalize the pressure on opposite sides of piston 63 to prevent chattering of valve '59 due to the Jill slight variations in pressure which occur between the suction and discharge strokes.

of pump cylinders 13 and 14. When the pressure is relieved slightly in pipes 73 due to the suction strokes o1" pump cylinders 13 and 14L, a slight amount of oil can leak through holes68 ,tomaintain' the effective pressure on the lower side of piston 63 in excess of the pressure on the discharge side so that valve 59 cannot leave its seat slightly and chatter. y

'lReferring now to Fig. 2, the purpose of the shield 80 is to protect packing 107 from the wearing action of leakage oil flowing through the operating valve when valve '85 is moved toward the right to effect the covering of openings 86. At this time shield 80 prevents to a considerable extent the leakage of oil through openings 86 out between the adjacent surfaces of valve 85 and sleeve 82. Any considerable leakage at this point would of course, tend to wear away packing 107. Also shield 80 serves to prevent wire drawing as the oil passes through openings 86 to discharge port 77,. The edge of sleeve 80 serves to sharplydefine the passae through openings 86. I

ith the above described arrangement a relatively unskilled person can operate the hydraulic press without the possibility of' requiring only the movement of operating handle 102.

In accordance with the provisions of the Patent Statutes, l[ have described the principle of operation of my invention, together with the apparatus which ll now consider to represent the best embodiment thereof, but desire to have it understood that the apparatus shown is only illustrative and that the invention may be carried out by other means.

What llclaim as new'and desire to secure by Letters Patent of the United States is:

1. In combination, an hydraulically operated device, a continuously running pump, a conduit connecting the pump to said device, a branch conduit leading from said first named conduit, and a fluid operated valve in said branch conduit which is normally open and is closed by fluid pressure to direct fluid from said pump to the device.

' 2. In combination, an hydraulically operated device, a'continuously running pump, ,a conduit connecting the pump to said device, abranch conduit leadlng from said ated valve in said circuit which whenclosed directs fluid to said device.

a. In combination, an hydraulically operated device, a continuously running pump, a conduit connecting the pump to said press, a branch conduit leading from said firstnamed conduit, a manually operated valve in said branch conduit which is normally open and is-adapted to be closed to direct fluid from said pump to the press, said manually operated valve being adapted to automatically open-when a predetermined pressure is reached.

5. In combination, a supply tank, a continuously running pump, a fluid circuit con necting the pump to the tank, an hydraulically operated device, a conduit connecting it to said circuit, a manually operated valve in said circuit, which when closed directs fluid from the pump to said device, and spring means which holds said valve and is adapted to yield to permit it to open when the pressure reaches a predetermined value.

6. ln combination, a supply tank, a continuously running pump, a fluid circuit connecting the pump to the' tank, an hydraulically operated device, a conduit connecting it to said circuit, a manually operated valve fluid from the pump to said device, a branch conduit connecting said first-named conduit to said tank, and a pressure operated valve which controls the flow of fluid through said branch conduit. a

7. In combination, an hydraulically operated device, a plurality of continuously running pumps for supplying fluid thereto,

fluid circuits for said pumps, conduits connecting said fluid circuits to said device, a manually operated valve in one of said fluid circuits, and a pressure actuated valve in another of said fluid circuits, said valves when closed acting to direct fluid to said device, said manually operated valve being adapted to open automatically when the pressure reaches a predetermined high value.

8. In combination, an hydraulically operated device, a plurality of continuously running pumps for supplying fluid thereto, fluid circuits for said pumps, conduits connecting said fluid circuits to said device, a manually operated valve in one of said fluid circuits, a pressure actuated valve in another of said fluid circuits, said valves when closed acting to d i rect fluid to said device, said pressure actuated valve being operated by the fluid pressure in the circuit contain ing the manually operated valve.-

9. In combination, an hydraulically operated device, a plurality of continuous y running pumps for supplying fluid thereto, fluid circuits for said pumps, conduits connecting said fluid circuits to said device, amanually operated valve in one of said fluid circuits, a pressure actuated valve in another of said fluid circuits, said valves when closed acting to direct fluid to said device, said pressure actuated valve being operated by the fluid pressure in the circuit containing the manuall v operated valve, and fluidpressure controlled means for rendering a pump inoperative when the pressure reaches a predetermined value.

10. In combination, a supply tank, a high pressure pump, a fluid circuit connecting it to said tank, a low pressure pump, a fluid circuit connecting it to said tank, an hydraulically operated device, conduit means connecting said fluid circuits to said device, valves in said fluid circuits, which, when closed, direct fluid to said device, and means controlled by the fluid pressure for rendering said low pressure pump inoperative when the pressure reaches a predetermined high value.

i 11. In combination, a supply tank, a high pressure pump, a fluid circuit connecting it to said tank, a low pressure pump, a fluid circuit connecting it to said tank, an hydraulically operated device, conduit means connecting said fluid circuits to said device, a manually operated valve in the circuit of one of said pumps and a pressure operated valve in the circuit of the other of said pumps, said manually operated valve when closed effecting the closing of said pressure operated valve to .cause fluid to be directed from both-pumps to said device.

12. In combination, a supply tank, a high pressure pump, a fluid circuit connecting it to said tank, a low pressure pump, a fluid circuit connecting it to said tank, an hydraulically operated device, conduit means connecting said fluid currents to said device, a manually operated valve in the circuit of one of said pumps and a pressure operated valve in the circuit of the other of said pumps, said manually operated valve when closed effecting the closing of said pressure operated valve to cause fluid to be directed from both pumps .to said device, and means controlled by the fluid pressure for rendering the lowpressure pump inoperative when the pressure reaches a predetermined high value.

13. In combination, a supply tank, a high pressure pump, a fluid circuit connecting it to saidtank, a low pressure pump, a fluid circuit connecting it to said tank, an hydraulically opera-ted device, conduit means connccting said fluid circuits to said device, a manually operated valve in the circuit of said high pressure pump, a pressure operated valve in the circuit of the low pressure pump, said high pressure pump supplying fluid to the device through such pressure operated valve, and said device exhausting through the pressure operated valve and the circuit of the low pressure pump to said supply tank.

14. In combination, a supply tank, a high pressure pump, a fluid circuit connecting it to said tank, a low pressure pump, a fluid circuit connecting it to'said tank. an hydraulically operated device, conduit means connecting said fluid circuits to said device, valves in said fluid circuits, which, when closed, direct fluid to said device, means controlled by the fluid pressure for rendering said low pressure pump inoperative when the pressure reaches a predetermined high value, and means for retarding the return of said low pressure pump to operative condition H after said fluid pressure is diminished.

15. In combination, a supply tank, a high pressure pump, a fluid circuit connecting it to said tank, a low pressure pump, a fluid circuit connecting it to said tank, an hydraulito said tank, a low pressure pump, a fluid circuit connecting it to said tank, an hydraulically operated device, conduit means connecting'said fluid circuits to said device, valves in said fluid circuits, which, when closed, direct fluid to said device, a suction valve for the low pressure pump, means controlled by the fluid pressure for holding said suction valve open when the pressure reaches a predetermined value, and means for retarding the closing of said suction valve after said pressure has been diminished.

17. In combination, an hydraulically operated device, a high pressure pump, a conduit connecting it to said device, "a low pressure pump, a conduit connecting it to said device, branch discharge conduits leading from each of said first-named conduits and through which the pumps normally pump fluid, a manually operated valve in one of said branch conduits, and a pressure operated valve in the other of said branch conduits, said valves when closed directing fluid, from both pumps to said device.

18. In combination, an hydraulically operated device, a pump such as 12, a conduit c0nnecting it to said device, a discharge pipe leading from said conduit, a valve 59 in said pipe, a pressure piston 63 for operating it, a source of fluid pressure connected to said pressure piston to operate the valve, and conduits such as 64: and 62 through which fluid is supplied from said source to said device.

19. In a system of the character described, a manually controlled valve comprising a casing having inlet and discharge openings, means forming an annular wall within the casing, a sleeve-valve which slides on said wall and is provided with openings adapted to be covered and uncovered by such wall, an operating means, and a yielding connection between saidv operating means and said sleeve valve.

20. In a system of the character described, a manually controlled valve comprising a casing having inlet and discharge openings, means forming an annular wall Within the casing, asleeve valve which slides on said Wall and is provided with openings adapted to be covered and uncovered by such wall, a cylinder connected to said sleeve valve, a piston therein, spring means forming a yielding connection between said cylinder and piston, and an operating member connected to said piston.

21. In a system of the character described, a manually controlled valve comprising a casing having inlet and discharge openings, means forming an annular Wall Within the casing, a sleeve valve which slides on said wall and is provided with openings adapted to be covered and uncovered by such wall, means for'moving sa1d sleeve valve, and a stationary shield member the end of which defines the area of the passage through the openings in the sleeve valve.

22. A manually controlled valve comprising a casing having inlet and discharge openings, means forming two spaced, annular, concentric walls within the casing, a sleeve valve located between said walls through which communication is established between said inlet and discharge openings, and means for moving said sleeve valve.

23. A manually controlled valve comprising a casing having inlet and discharge openings, means forming two spaced, annular, concentric walls within the casing, a sleeve valve located between said walls through which communication is established between said inlet and discharge openings, an operating handle, and a yielding connection be- .tween said sleeve valve and said handle.

24. In a syste of the character described, the combination with a continuously running pump, an hydraulically operated device, a conduit connected to. said device, a pump conduit, and a discharge conduit, of a valve structure such as 24 for connecting said first-named conduit to either the pump conduit or the discharge conduit, said valve structure comprising a casing with which said conduits are connected, a normally open valve controlling communication between said flrst-named conduit and said discharge conduit, and a normally closed valve controlling communication between said firstnamed conduit and said pump conduit said valves being actuated by fluid pressure from said pump and said normally closed valve having a leakage passage around it.

25. In a system of the character described, the combination with a high pres- 7 sure pump, a low pressure pump, an hydraulically operated device, a conduit connected to said device, a low pressure pump conduit, a high pressure pump conduit and a discharge conduit, of a. valve structure for controlling the connections among said conduits comprising a casing with which said conduits are connected, a normally open valve therein which, when open, connects said first-named conduit and said low pres sure pump conduit to said discharge conduit and when closed cuts off communication between such first named conduit and the discharge conduit, a piston for operating said valve which is subjected to the pressure from the high pressure pump, and a normally closed valve which, when opened, connects said high pressure pump conduit to said first-named conduit.

26. In a system of the character described, the combination with a high pressure pump, a low I pressure pump, an hydraulically operated device, a conduit connected to said device, a low pressure pump conduit, a high pressure pump conduit and a discharge conduit, of a valve structure for contifoiiing the connections among said conduits comprising 2i casing with which said conduits are connected, a normally open vaive therein which, when open, connects said first-named conduit and said low pressure pump conduit to said discharge conduit and When closed cuts off communication between such first-named conduit, and the discharge conduit, 2i piston for operating said 10 valve which is subjected to the pressure ee-13cc 

